During reprocessing of nuclear fuel, separated high-level waste material must be treated and stored so as to prevent spreading into the biosphere. The first stage is to transform the waste into a solid state and to, for example, convert it into a solid, crystalline material having good chemical resistance and good resistance to leaching by water. One way of achieving this is to compress, at a high temperature and a high pressure, a mixture of waste and a resistant material in particulate form into a massive, solid body where the active material becomes permanently bound. A method of achieving such a solid body is disclosed in U.S. Pat. No. 4,172,807. Radioactive metal scrap or radioactive ashes may be treated in a similar manner.
A problem when transforming the waste into a solid state is the contamination of the equipment used in the process. In the method according to the abovementioned patent, containers may be filled with waste material in particulate form and sealed in a relatively simple manner. The equipment used for the filling and the sealing is relatively simple and may therefore be cleaned in a simple manner prior to any necessary repair work. The furnace equipment for the hot pressing, on the other hand, is complicated and much more difficult to clean after a possible contamination.